This interview gives some insight -
“ The way it works within Google is that it’s one massive source tree, one root, and one unified build system across all of it. And so anyone can go and change anything. But there are code reviews, and directories have owners, always at least two people, just in case someone quits or is on vacation.
To check in you need three conditions met: You need someone to review it and say it looks good. You need to be certified in the language – basically, you’ve proven you know the style of this language – called “readability.” And then you also need the approval from somebody in the owner’s file in that directory. So in the case that you already are an owner of that directory and you have readability in that language, you just need someone to say, “Yeah, it looks good.” And it’s a pretty good system, because there tends to be a minimum of two, up to twenty, thirty owners. Once you work on a code base for a while, someone just adds you to owners. I think it’s a great system.”
Pretty good !
